Reduce the File Size of PDF Documents with Preview in Mac OS X

The PDF file format is ubiquitous for good reason, mostly because it allows for perfect preservation of a documents formatting, text, and other elements, but also because it allows for encrypted password protection of documents. But let’s face it, sometimes PDF files can be bloated, and something that should be 200k or less can be 1.2MB for no obvious reason, particularly if they have been generated at the OS level from something like printing to a PDF, another file that has been converted to a PDF, or created with an app that just doesn’t offer any compression at all.

This article will show you how to reduce the file size of PDF documents using tools included in Mac OS Preview app, which is bundled by default on every Mac. The shrinking of the PDF file size can be very effective and dramatic, so if you need a notable reduction in PDF file size this guide should be of great assistance to you.

Let’s get to it and learn how to reduce the file size of a PDF on the Mac.

How to Reduce PDF File Size on Mac with Preview

Open the PDF file that you want to reduce the size for in Preview app (typically Preview is the default PDF viewer in Mac OS X * but if not you can find it in the /Applications/ folder of Mac OS)

Pull down the “File” menu and choose “Export”

Select the submenu next to “Quartz Filter” and choose “Reduce File Size”

Save the new reduced version of the PDF as usual by hitting “Save”

(Note: you can also access Quartz Filters through “Save As” with new versions of Preview for Mac OS, but the File > Export trick works for prior versions of the app as well. Additionally, if you don’t need a color document then choosing “Greyscale” as the filter can also dramatically reduce the file size of a PDF document)

Just how much space you will save by using this file reduction filter varies greatly, depending on the content of the PDF, the original app that created and saved the PDF and if any filtering was applied to begin with, amongst a variety of other factors. For originating documents that are entirely text, like a resume or a Word document that’s been converted to a PDF without any sort of optimization, it can make a huge difference, and you may see a file sized from 1MB shrinking down to under 100k.

Keep in mind that Quartz Filters are basically image processing filters, but unlike apps made for lossless image compression, the PDF file will be processed in such a way which may result in lossy compression and artifacts appearing on embedded imagery. That’s not always desirable, which makes this trick best for PDF files that are heavy on text, simple graphs, charts, spreadsheets, or basic vector drawings, and not complete images or photos where high image quality is desired. Again, this is a benefit to using the “Export” command, since you can compare the two documents easily when it’s finished, which is recommended. You don’t want to overwrite the original PDF file with the compressed version without knowing if the quality is up to the standard you require.

For PDF files that have not been optimized yet, the Preview app in Mac OS X can often reduce the file size considerably by passing it through an export filter as described, sometimes shrinking a document by 40% or even more than 90% depending on the PDF file and the contents. This works particularly great for shrinking the size of text heavy PDF files, but it’s not a perfect solution for every document out there, so you’ll want to run through the process with the document in question and compare it to the original PDF to see if it helps or if the quality of the outputted reduced PDF file is sufficient for your needs.

Counterintuitively and in some less common situations, beginning with an already optimized and compressed PDF file may result in a larger file being generated using this reduction filter. This really depends on the application that created the PDF to begin with and if the file was compressed at all, but for situations where a PDF is generated through something like Adobe Acrobat Pro you may find it to be the case.

Regardless, you might want to get the file size of the documents in question both before and after the compression. On the Mac that’s quite easy to do with the “Get Info” command, selecting the PDF file in the Finder and going to the “File” menu to choose “Get Info”.

This trick will work in basically all versions of Preview on all versions of Mac OS system software, whether it’s in macOS Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion, Snow Leopard, etc.

Was this trick effective for you to shrink a PDF file? Do you know of another method of compressing PDF files or shrinking down a PDF document to reduce the file size? Share your experiences and information in the comments!

I found that the compression in Preview doesn’t work well for scanned documents with text and/or figures as it indeed compresses the image too much and the text/figures become blurred. What worked for me was opening the scanned document in Preview, whether it was jpeg or pdf, then going to File/Take Screenshot/Selection, selecting the page, taking a screenshot, then again going to File and selecting Export as PDF for the screenshot document. That then brought my scanned documents down from around 10MB each to around 350KB and the figures were still clear and readable.

I had a 12 page scanned PDF document that was 3.2MB and this method reduced it to ~250kb – amazing! But then I opened the file up and it was extremely fuzzy, to the point that the text was unreadable. Looking for a better solution.

The issue I had was that a 20mb pdf (derived from a 40mb png file from a scanner) was reduced to a 20kb file that was very grainy, albeit perfect for viewing as an icon, not so good when using it as a scanned building layout.
My solution was to scan the 8″x11″ document in a lower resolution (300x300dpi) then converting it to pdf. The size was a reasonable 5.5mb afterwards.

This reduced a file from 4MB down to 38kb—way too small. I tried to find a way to change the default setting but couldn’t do it. I wonder what happened to the “save as” key?? (I just upgraded to Mavericks from Snow Leopard)

This website and third-party tools use cookies for functional, analytical, and advertising purposes. By continuing to browse the site, closing this banner, scrolling this webpage, or clicking a link, you agree to these cookies. You can review our privacy policy for additional information.I AcceptPrivacy Policy